Electric circuits, comprinsing electric discharge devices



J. M 'l. FERGUSON ELECTRIC CIRCUITS COMPRISING Filed June 22, 1948 9W: 0 W2. fm amw fig al-cad, M

Patented Nov. 15, 1949 Erecting creams, COMPRISING 'ELECTRICDISCHARGE DEVICES Jdhh mciniyi riguson, Stafford, England, assignor to The English Electric Company Limited, London, England, a British company Application June 22, 1948, Serial No. 34,478 In Great Britain June 24, 1947 This invention relates tqan electric circuit comprising an electric discharge device of 'tlie mercury pool cathode type. This circuit is p rticularly applicable for the; purpose of pulse modulation in a radar transmitter v The electric circuit according to the invention comprises an electric discharge .devicehavingfa mercury pool cathode, Qmea s to init'iate an arc therefrom, and at least twoanodes provided ith independent control electrodes, one ofsaidan des being connected in series with the primary ing of a step-up transformer to discharge a capacitance therethrough, and thereby to charge to a high voltage a second capacitance connected to the secondary winding, and the second of said anodes being connected across the 'secondary winding to discharge the second capacitance through a load, and meanstoapply. positivepulses to the control electrodes in rapi'cl succession" so that the arc to the second anode is established either before or shortly after that to the "fiifst anode has ceased, and to repeat these pul'sesfso that the cycle of charge and discharge of the capacitances is repeated at high frequency.

The accompanying drawing shows a diagrammatic representation of a pulse-modulatingoiricuit which embodies the invention in preferred form.

The mercury pool discharge device I flhas three anodes H, i2 and I3, each in a separate anode arm, and a single mercury pool cathode iii, An igniter i of conventional form dips into the cathode pool. V

The igniter l5, and also anode [2 which serves to provide an excitation arc, are both supplied from a D. C. source 2% through a choke 2!. The supply of current between the igniter l5 and this source is controlled by pushbutton 22 and it flows through; resistor 23 which limits the current. When ignition is effected by depressing push button 22, the excitation arc from cathode pool as to excitation anode 12 becomes established, and the current in this are is limited by resistor 24.

When the excitation arc has been established, an arc will occur from cathode pool [4 to anode ii when this anode is positive and a control grid E6 in the same anode arm is given a sufiicient positive pulse. Thereafter the are between cathode pool l4 and anode H is sustained until the positive voltage of anode I relative to cathode pool Hi falls to a low value. The initiation of an arc between the cathode pool l4 and anode I3 is likewise controlled by grid l1.

Condenser is charged from a direct current 5 source 3| through a choke 32. When condenser Bil-has been charged, a positive firing pulse applied between terminal M] and earth overcomes the negative bias given by direct voltage source t], and condenser 3B discharges through the primary winding 33 of a step-up transformer 34, and between anode H and cathode pool M. The pulse of current through primary winding 33 thus produced induces 'a pulse of current in seclondary winding 35 of transformer 3 and'the'reby charges an artificial line network 36 through a load represented as resistance 37. The impedance presented by artificial live network 36 iseffe'c tively a capacitance. a, A

At a controlled delay period after the positive pulse is applied between terminal fill-and earth, another positive firing 'p'ulse is applied between terminal and earth, sufiicie'nt to overcome the bias obtained from source 5i and thereby to initiate an are between cathode pool ['4 and anoqe I 3. This are establishes a discharge circuit-for network 36 through 10m 37', and continues until network 36 has so far discharged that the voltage between anode l3 and cathode pool I 4 is no longer sufiic'ient to maintain an arc. b

When the are between anode H and cathode M has ceased, the charging of condenser 39 "from source 3| immediately reconn'nences and the Whole cycle of operation is repeated.

The :voltage of source 20' which supplisthe igniter l5 and the excitation anode 12 may b'e'60 volts. Resistor 23 may have a value of about 10 ohms, and resistor 24a1soa value about 10 ohms so that the excitation current from anode I2 is limited to about 4 amps. I M

Bias source 4| may have a value of about "4'60 volts and the positive firing pulse-'applied atter min al Ml may be of about 1000 volts witha diira tion of about 10 microseconds. Resistor 32, which limits the grid current, may have a value of '500ohms. I, a l a Bias source 5| may have a value of about 600 volts and the positive firing pulsea'pplie'd' at terminal 50 may be again of about 1000 volts with a duration of about 10 microseconds. Resistor 52, which limits the grid current, may have a value of 2000 ohms. The interval between the firing pulses applied at terminals 48 and 50 may be about 300 microseconds.

In some cases it is desirable or necessary that the arc to anode It be started before that to anode I2 has ceased. In other cases, however, the arc to anode l3 may be started shortly after that to anode I2 has ceased, though the interval will never exceed about microseconds.

The apparatus may be operated in a circuit drawing 20 amps. from a source 3! which may be of 350 volts. With a 25:1 step-up transformer ratio, voltage peaks of 20 kilovolts can be established on network 36, discharging through a load 31 of surge impedance 20 ohms giving kv. pulses, 500 amps. for a 2 microseconds duration with a variable repetition frequency of 250-1000 cycles.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electric circuit comprising an electric discharge device having a mercury pool cathode, means to initiate an arc therefrom, and at least two anodes provided with independent control electrodes, one of said anodes being connected in series with the primary winding of a step-up transformer to discharge a capacitance therethrough, and thereby to charge to a high voltage a second capacitance connected to the secondary winding, and the second of said anodes being connected across the secondary winding to discharge the second capacitance through a load, and means to apply positive pulses to the control electrodes in rapid succession so that the arc to the second anode is established either before or short- 1y after that to the first anode has ceased, and to repeat these pulses so that the cycle of charge and discharge of the capacitances is repeated at high frequency.

2. A circuit according to claim 1, wherein an additional anode is provided to serve as excitation anode.

3. A circuit according to claim 2, wherein the arc to the excitation anode is initiated at the commencement of operation by means of an igniter dipping into the mercury pool.

4. For producing very heavy current pulses of very short duration at a repetition frequency of the order of hundreds of cycles per second, an electric circuit comprising an electric discharge tube having a mercury pool cathode, a first anode provided with a first control grid, a second anode provided with a second control grid, and means to establish a continuous excitation arc in the tube; a first capacitance connected in series with a first impedance between the first anode and the cathode, a second capacitance connected in series with a second impedance between the second anode and the cathode, means to charge said capacitances at said repetition frequency, and means after said capacitances are charged to'apply firing pulses to the first and second control grids at an interval of the order of hundreds of microseconds, the parameters of the circuit of the first anode being such that the discharge of the first capacitance through the first impedance initiated by the firing pulse upon the first control grid will subsist at least until the application of the firing pulse to the second control grid, and the parameters of the circuit of the second anode being such that the discharge of the second capacitance through the second impedance will produce a very heavy current pulse through the second impedance subsisting only for a period of the order of microseconds.

5. A circuit according to claim 4, wherein an additional anode is provided for the continuous excitation arc.

6. A circuit according to claim 5, wherein the arc to the excitation anode is initiated at the commencement of operation by means of an igniter dipping into the mercury pool.

7. A circuit according to claim 4 wherein the said first capacitance is charged through a choke from a direct current source.

8. For producing very heavy current pulses of very short duration at a repetition frequency of the order .of hundreds of cycles per second, an electric circuit comprising an electric discharge tube having a mercury pool cathode, a first anode provided with a first control grid, a second anode provided with a second control grid, and means to establish a continuous excitation arc in the tube; a first capacitance connected in series with a first impedance between the first anode and the cathode, a second capacitance connected in series with a second impedance between the second anode and. the cathode, means to charge said capacitances at said repetition frequency, and means after said capacitances are charged to apply firing pulses to the first and second control grids at an interval of the order of hundreds of microseconds, the parameters of the circuit of the first anode being such that the discharge of the first capacitance through the first impedance initiated by the firing pulse upon the first control grid will subsist until a time not more than microseconds before the application of the firing pulse to the second control grid, and the parameters of the circuit of the second anode being such that the discharge of the second capacitance through the second impedance will produce a very heavy current pulse through the second impedance subsisting only for a period of the order of microseconds.

9. A circuit according to claim 8, wherein an additional anode is provided for the continuous excitation arc.

10. A circuit according to claim 9, wherein the arc to the excitation anode is initiated at the commencement of operation by means of an igniter dipping into the mercury pool.

11. A circuit according to claim 8, wherein the said first capacitance is charged through a choke from a direct current source.

JOHN McINTYRE FERGUSON.

REFERENCES CITED The following references are of record in the file of this patent: 

